question_answer 19)

A magnetic field set up using Helmholtz coils (described in Exercise 4.16) is uniform in a small region and has a magnitude of 0.75 T. In the same region, a uniform electrostatic field is maintained in a direction normal to the common axis of the coils. A narrow beam of (single species) charged particle all accelerated through 15 kV enters this region in a direction perpendicular to both the axis of the coils and the electrostatic field. If the beam remains undeflected when the electrostatic field is, make a simple guess as to what the beam contains. Why is the answer not unique.  

Answer:

Using , we get                                                 Also                 or                                  The given particle may be deutron.                 The result is not unique because this e/m ratio can be true for etc.